Conventionally, a breather device preventing the confinement of pressure within a transmission case, particularly in a vertically mounted transmission for front engine rear drive (FR) vehicles mounted in vehicles such as 4WD off-road vehicles, should prevent breather blow, and form a labyrinth structure within the transmission case, in which an exit side of the labyrinth structure is structured to open to outside air via a breather pipe through a breather plug provided on a front upper portion of the transmission case, on the assumption that large forward and rearward tilting occurs in the transmission case when the vehicle is traveling.
In recent years, improvement of the driving performance of 4WD off-road vehicles such as the above has been demanded, and a breather device capable of supporting travel under severe circumstances such as 45° slope roads is becoming necessary.
However, with a conventional breather device such as the above, the possibility remains that breather blow may be generated by the agitation of oil from a rotating member in an inner portion of the transmission during travel on a slope road, particularly travel down a slope road. Fundamentally changing the breather device could be considered as a solution to this breather blow, however, such a large change would invite huge cost increases. In addition, a solution to breather blow would inevitably be accompanied by an increase in the size of the transmission exterior such that mountability in a vehicle is worsened.
Hence, it is a primary object of the present invention to provide a breather device for a transmission realizable with minimum alterations to the conventional transmission case, that prevents breather blow during vehicle travel on steep slope roads. In addition, it is a further object of the present invention to enable the realization of preventing breather blow on a steep slope road without increasing the size of the transmission exterior in practice.